Health officials say Tung Shen Wu — also known as David Wu — was practicing dentistry illegally in the bedroom …

Warnings about a Vancouver-area man operating an unlicensed, unsanitary dentistry practice out of an apartment highlight's Canada's problem of underground medical practitioners who prey on the poor and on immigrants.

Tung Sheng Wu, who also goes by David Wu, is in trouble with health authorities and the B.C. College of Dental Surgeons after being exposed as a bogus dentist for the second time in a decade, CTV News reports.

The college, supported by RCMP investigators, raided a suburban Burnaby apartment last May and found a clandestine dental office set up in one of the bedrooms, along with files for 1,500 patients, the Vancouver Province said. Some were from as far away as Washington state.

Those people now are being urged to come forward and be tested for blood-borne diseases such as hepatitis B and C and HIV.

Authorities said Wu, who has no connection with a legitimate Burnaby dentist named David Wu who retired in 2010, had been operating out of the apartment for 10 years but may have been practising dentistry illegally as far back as the 1990s.

He was exposed once before, in 2003, while operating out of a home in suburban Port Moody. The B.C. Supreme Court issued an injunction barring him from saying he was a dentist, CTV News said. Wu supposedly promised to leave the country, but didn't.

“He is neither qualified nor competent to practice dentistry in British Columbia. We do not know what, if any dental training he has,” college CEO Jerome Marburg told a news conference Wednesday.

“Evidence obtained indicates that he has used materials not approved by Health Canada, and that he did not follow infection control precautions for the cleaning and sterilization of his dental equipment and supplies.”

Marburg said the college was tipped Wu, who had no known training, was back in operation by a disgruntled patient. The college then hired a private investigator to stake out Wu's home clinic, Global News said.

Fraser Health Authority medical health officer Dr. Michelle Murti said an inspection of Wu's makeshift clinic showed a "gross lack of basic hygiene," the Province reported. There was evidence he didn't sterilize his equipment, including syringes that reused.

Wu's files indicate at least one third of his clients were children.

Wu is scheduled to make a court appearance on Monday, CTV News said.

A Toronto Star investigation four years ago revealed illegal dentistry is a thriving underground industry within immigrant communities.

Bogus dentists take advantage of newer arrivals who often have no money or dental insurance, the Star found. It's estimated almost one third of Canadians don't have dental insurance. Immigrant patients told the Star this was how they got dental treatment back home.

A seven-year-investigation by the Royal College of Dental Surgeons of Ontario turned up 42 phoney dentists, the Star said.

One operator tracked down by the Star had no apologies.

“I know it is illegal,” Mikhail Genkin said after a Star reporter posing as a patient identified herself. “I think I help people because my price is very low and quality is quite good.”

That's generally not true, said the college's registrar. Irwin Fefergrad told the Star patients at unregulated dental practices are vulnerable to complications, including infections from unsterilized tools. There's also a danger that radiation from unshielded X-ray machines can pass through the ceilings and walls of these home clinics.

While essential medical treatment is covered under provincial medicare plans, patients pay for dental work in cash or via private insurance.

Elective cosmetic surgery is also not covered, driving some people to underground practitioners.

This Magazine published an in-depth look at one clandestine plastic surgery in 2010, profiling a young woman who had labia-reduction surgery performed by a man who does body piercing for a living.

The procedure, performed in the guy's apartment, didn't go well. The "patient" experienced pain and serious post-op bleeding. A subsequent examination in hospital revealed the beginnings of an infection. The "surgeon" was arrested and later committed suicide.

Police in Toronto are also dealing with a continuing problem of women seeking buttock enhancements via injections delivered by unqualified practitioners.